Heatless adsorption

Separation of Hydrogen Sulfide-Hydrogen Mixtures by Heatless Adsorption... 

Cyclic adsorption processes such as parametric pumping, cycling zone adsorption and heatless adsorption have received much attention both theoretically and experimentally in the past several years (3j. Skarstrom (4J has reviewed applications of heatless adsorption (synonymous with pressure swing adsorption) to air drying, hydrogen purification and air fractionation. 

Stewart and Hack (5.) have presented operating characteristics of pressure swing adsorption systems for reducing impurities in a hydrogen stream from 40 vol percent to 1 ppm. Impurities included ammonia, water, methane, carbon monoxide, carbon dioxide, nitrogen, and several hydrocarbons. In this study heatless adsorption is used to separate hydrogen sulfide-hydrogen mixtures and the experimental results are compared with theoretical models. 

Heatless adsorption is a cyclical process for the purification of gaseous mixtures by the separation of the gas into two streams. One stream which contains more of the more strongly adsorbable materials is called the purge. The other process stream is called the product stream and contains less of the more-adsorbable components. Pressure reduction during the purging cycle coupled with the use of product purge gas and short cycles allows the process to operate without the use of heat for bed... 

A duo-bed heatless adsorption cycle has been described by Shendalman and Mitchell (6). The cycle consists of four distinct steps (Figure 1). 

Separations of hydrogen sulfide from hydrogen were achieved in a continuous manner using the heatless adsorption process. 

Although the purpose of this investigation was to study the initial transient behavior of heatless adsorption, the best removal of hydrogen sulfide occurred in the run with 3.01% H S and a y = 2.88, cycle time of 12 minutes and feed rate of 190 sCCM. Removal was down to 99.55% in three hours. For the 6.32% feed the best removal for the same time period was 98.49%. 

The most common feed rate in this study is also shown in Figure 9. The feed rate of 190 SCCM at high pressure is shown to take approximately 2.5 hours for the product concentration to reach that of the feed. The low pressure feed takes a shorter time of about 1.5 hours. These runs were conducted after the heatless adsorption runs and indicate no significant deterioration of the adsorbent had occurred during the course of the experiments. 

Whitley, M.D., "Separation of Hydrogen Sulfide-Hydrogen Mixtures by Heatless Adsorption", MS Thesis, University of Kentucky, 1975. 

Processes involving total-pressure reduction to remove the adsorbed species, called pressure-swing adsorption (PSA) or heatless adsorption, are mechanically complex, since they must include separate adsorption, depressurization, desorption, and repressurization steps. To accommodate a steady flow of feed and products, several beds - usually three or more in parallel -are used. A typical four-bed process flowsheet is shown in... 

The two-column process (Figure 2) is the heatless adsorption process of Skarstrom (5 ) This process can perform both recovery and purification of a light component Local equilibrium models of this process have been presented by Shendalman and Mitchell (6), Chan et al (7), and Knaebel and Hill (8) In each case the method of characteristics was used. Models with finite mass transfer rates have been published by Kawazoe and Kawai (9 ), Mitchell and Shendalman (10), Chihara and Suzuki (11), and Richter et al (12). In these models the method of characteristics and direct integration of partial differential equations were employed ... 

Two-Column Process The heatless adsorption process (Figure 2) has two columns Each column undergoes a four-step cycle. Three steps involve the same sequence as the single column process pressurization with feed, feed at high pres-... 

Such a process was originally known as heatless fractionation or heatless adsorption since no heat was used to regenerate the adsorbents. Currently the term... 

Knaebel, K.S. and F.B. Hill, Analysis of gas purification by heatless adsorption", AlChF National Meeting, Los Angeles, CA, Nov. 14-18 (1982), paper 91d. 

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